There are many applications where it is necessary to dispense a liquids at a desired rate. In agriculture for example liquid chemicals such as pesticides, fungicides, and herbicides are applied to crops or field surfaces through spray nozzles mounted on a spraying vehicle. Agricultural sprayers then must accurately dispense the liquid over the desired area of target surface. This has typically been accomplished by providing a spray nozzle having a set operating pressure such that when operated at that pressure, the nozzle accurately dispensed a known amount of liquid per time unit, or known flow rate. Operating the sprayer at a known speed then accurately resulted in the correct amount of fluid being dispensed over a given area, however if the sprayer speed increased or decreased the application rate decreased or increased accordingly.
The nozzles are spaced apart on a sprayer boom, perpendicular to the direction of travel, at a standard spacing distance which corresponds to the spray pattern of the nozzles. The same size nozzle is in operating position at each nozzle location, providing a consistent application rate across the width of the sprayer. The most common spray pattern is a flat-fan pattern, and the nozzles are generally rotated approximately 10 degrees from being perpendicular to the direction of travel in order that the overlapping spray patterns do not intersect and interfere with each other. In order to provide a spray pattern that provides satisfactory full coverage of the target area being sprayed these sprayer nozzles are limited to operation within a specified pressure range, typically for example 20-60 pounds per square inch (psi). To provide an application rate outside the specified pressure range, the nozzles are changed.
Rate controllers are available which measure the total flow of fluid along the boom to the nozzles and automatically vary the pressure as the speed varies, maintaining a total flow to the nozzles that will maintain a stable application rate along the boom as speed varies. These rate controllers can also be used to vary the application rate by maintaining a constant speed, and varying the pressure. Variable application rates have become desirable with the advent of field mapping, where different areas of a field are best treated with different rates of the particular liquid being applied.
Modern agriculture/horticulture sprayers typically have a boom with multiple spray sections that can be independently controlled. Usually a master control means is used to control the entire boom, while each section may have its own control or switch. Liquid pressure in each section can be varied by a rate controller to apply different rates to field portions passed over by each section, and flow to any section can be stopped completely if desired.
Also in agriculture liquid fertilizer is dispensed through nozzles that do not provide full coverage, but rather simply drop the liquid fertilizer into a furrow or dribble the liquid onto the ground. A typical liquid fertilizer applicator will comprise a ground driven pump supplying pressurized liquid to a plurality of spaced apart nozzles that dispense a stream or streams of liquid onto the ground. There is no requirement for a defined spray pattern so the pressure can vary more widely. The nozzles define an orifice or orifices of a known size such that they dispense a known rate at a known pressure. With a ground driven pump the pressure varies with speed so at a lower speed the pressure is lower and the rate of flow through the nozzles is lower, and the application rate per unit of area remains substantially constant as speed varies. Hydraulic drive pumps are also commonly used with a control system that controls pressure as speed varies. Liquid fertilizer application is commonly done at the same time as seeding, with the nozzles mounted on the seeding implement and a liquid fertilizer tank pulled behind. It is also known to apply liquid fertilizer using the conventional full coverage spraying equipment used for spraying herbicides, pesticides, however apply liquid fertilizer to a growing crop with full coverage nozzles can damage the crop and so it is common to change the type of nozzles used to nozzles that dispense a stream of liquid.
External location and guidance systems utilizing Global Positioning Satellites (GPS), local broadcasting towers, and the like have allowed sprayers to be located and also guided precisely, and also provide precision control of application rates and avoidance of spray overlap as described for example in U.S. Pat. Nos. 6,522,948 and 6,877,675 to Benneweis.
Considerable precision in the controls is desirable, as discussed in U.S. Pat. No. 8,352,130 to Mitchell which provides a system for anticipating a change in the ground speed of the spraying vehicle such that a lag that otherwise would occur in the rate of product input delivered is reduced.
An externally guided spraying system is also described in U.S. Pat. No. 7,124,964 to Bui which discloses a flexible, self-adjusting flow nozzle where the self-adjusting capability of the spray nozzle enables the creation of an automatic spray system that includes a computerized controller that receives inputs pertaining to vehicle speed, geographic vehicle position, and flow rate and/or fluid pressure which are compared against a predetermined flow plan for a given field and the controller automatically adjusts the flow rate to the nozzles accordingly.
U.S. Pat. No. 7,874,197 to Jackson, et al. discloses an apparatus for manually measuring a rate of liquid flow through a spray nozzle includes a container with an opening in a top thereof adapted to receive a liquid discharge from a spray nozzle.
U.S. Pat. No. 7,395,769 to Jensen discloses a farm implement for applying a product to a row crop or a row seeded field wherein the implement has a plurality of spaced-apart product dispensers, such as spray nozzle, seed dispensers, and the like, where each of dispenser is individually automatically controlled by an external guidance system. The application rate of each dispenser is adjusted to compensate for the different ground speeds encountered during turns, and also to vary application rates according a field map indicating desired application rates for different field areas. Achieving a wide range of smoothly transitioning application rates with current spray nozzles is, however, problematic.
U.S. Pat. No. 6,126,088 to the present inventor Wilger discloses a nozzle mounting and control system for use in sprayers comprising multiple nozzles mounted in the operating position on a sprayer boom such that 2, 3, or more nozzles pass over the same target surface. Wide ranges of application rates are achieved by control valves operable to select which nozzles are open and operating at any given time. The valves may be remote controlled and may further incorporate a rate controller to maintain a chosen application rate by opening and closing appropriate valves as the sprayer speed varies, and/or by varying the pressure in the conduits supplying the nozzles.